At present, locomotives in which power is generated by an internal combustion engine (generally a diesel engine) include one or more axial fans for ventilating radiators, i.e. cooling them by means of a flow of air, which radiators may themselves be heated either by means of a cooling fluid such as water, or else by means of the oil which is used to lubricate the engine.
Two dispositions are commonly used:
either the fluid-cooling heat exchangers are disposed vertically in layers above the locomotive chassis, in parallel with its side faces and pressed thereagainst or set back slightly therefrom; or else
the heat exchangers are placed in horizontal layers in the proximity of the locomotive roof.
When using side heat exchangers, the axial fans are disposed with their axes extending vertically and the fan diffusers, or sometimes even their air-guiding shells are housed directly in openings passing through the locomotive roof. The fans then suck ambient air through the heat exchangers.
When the heat exchangers are placed in horizontal layers close to the locomotive roof, the axial fan or fans are placed beneath the layer of heat exchangers. They are generally mounted about vertical axes and blow air towards the heat exchangers, with the ducting between the fan shell and the heat exchangers flaring from a small circular cross-section at the fan end to a larger rectangular cross-section at the heat exchanger end.
In either case, it is essential to remove all obstacles from the volume close to the propeller suction zone if the ventilation is to operate properly, and where possible the suction streamlines should be guided by deflectors.
In the second variant, the vertical extent of the air duct between the fan and the heat exchangers must be sufficient to ensure that the air flow is as uniformly distributed as possible in spite of the flow beginning with a circular cross-section and subsequently cooling a rectangular area.
In either case, the installation for cooling the internal combustion engine as described above is bulky and requires not only a large amount of space for its own equipment per se, but also for suitable air passages in its immediate vicinity. In order to ensure that an axial fan operates with adequate efficiency, it is essential for the streamlines of the intake air and of the outlet air to be as near as possible parallel to the propeller axis.
It is common practice to use propellors of large diameter (e.g. 1 meter to 1.5 meters) in order to reconcile the following conditions as well as possible:
rectangular heat exchangers should be ventilated as well as possible;
maximum advantage should be taken from the greatest available width in the locomotive (while leaving adequate cross-sections for the necessary longitudinal passages); and
as small as possible a number of fans should be used, in order to keep costs acceptable.
When the internal combustion engine is operating at full power, such large diameter fans frequently need to turn at 1500 to 2400 revolutions per minute (r.p.m.).
Measurements performed on stationary locomotives having diesel engines which have not been specially sound-proofed (no exhaust silencers, no silencing coating on the engine compartment walls) have shown that the noise audible outside the locomotive due to the cooling fans is often equivalent to that due to the engine itself. Such fans are thus a major source of noise power. Further, the air intake is located close to the bottom of the locomotive in a region where the air is relatively polluted, in particular by dust and by vapor from liquid fuel.
When ventilating the starting and braking rheostats used on locomotives having electric traction drive (e.g. electric locomotives or diesel-electric locomotives), it is general practice to use a variant in which the axial fans blow air over the rheostat resistances. However the same drawbacks of noisy operation and intake of relatively polluted air re-occur.
The aim of the present invention is to provide devices for ventilating the fluid radiators associated with an internal combustion engage in a locomotive, and/or the starting and braking rheostats associated with a locomotive having electric traction, while generating less noise than current devices, while occupying less volume and while providing the same cooling efficiency.